Trump promised to make the economy better. Is he able to do that remains to be seen, but his message was pretty clear, and he did have some success before COVID in that regard. Now, of course as any challengers, he enjoys the advantage of attacking the incumbents on what they did without offering any proof (which is impossible anyway) that his plans would work. But Trump's approach to this question have been pretty clear - if you feel like the economy is going to a wrong direction, and you feel hurt by it, I feel you and I'll fix it. Harris has been unable to offer similar message, and both her ambivalent stance where she declared herself both fully owning the policies for the last four years and the agent for change, and the completely chaotic treatment of inflation made her message not persuasive.
I think the big issue is that Harris knows she’s making empty promises and doesn’t like to do that. She also know that the problems were in fact caused by the policies made 4 years ago.
Trump knows he’s making empty promises but doesn’t give a shit as long as it wins him the presidency, he’ll wing it all later, and people won’t remember that he didn’t keep his promises because they only care that he said he would try.
It was something about people remembering how you made them feel, instead of exactly what you did.
Trump's "success" before 2020 was due to him intimidating the Fed into not ending QE.